1. Field of the Invention
The present invention relates to an alarm system, and more specifically to an alarm system capable of performing alarm action according to the operation of a transmitter.
2. Description of the Related Art
As one of vehicle security systems, a vehicle alarm system that causes a horn and headlights to perform intermittent working (hereinafter referred to as alarm action) by using a receiver installed in the vehicle in response to the operation of a transmitter at hand has been proposed. In one of vehicle alarm systems of this type, an alarm reversal signal is transmitted from the transmitter every time a switch of the transmitter is operated, and the receiver installed in the vehicle alternately activates and deactivates the alarm action upon receipt of each alarm reversal signal. For example, the alarm system is used when the driver of a vehicle sees a suspicious character near the vehicle. In such a case, the driver makes the vehicle activate the alarm action by operating the transmitter at a distance from the vehicle and thus scares the suspicious character away, to thereby prevent the theft of the vehicle and the like.
In the above-mentioned vehicle alarm system, however, the activation and deactivation of alarm action are controlled by operation of a common switch, so that the operator who operates the switch cannot recognize the switching status (activation or deactivation) of alarm action without thinking on the basis of switch operation, and is liable to carry out wrong operation. For example, there is the fear that the wrong operation delays the deactivation of alarm action, which annoys the people around.
Given this factor, U.S. Pat. No. 4,232,308 proposes a vehicle alarm system in which different operation modes of a switch are provided in order to distinguish between the activation and deactivation of alarm action. In this vehicle alarm system, an alarm-ON signal is transmitted from the transmitter when the switch is pressed for a relatively long period of time, and the receiver that receives this alarm-ON signal activates alarm action. If the switch is pressed for a relatively short period of time, an alarm-OFF signal is transmitted from the transmitter, and the receiver that receives this alarm-OFF signal deactivates the alarm action.
Compared to the former vehicle alarm system that transmits and receives a single alarm reversal signal, the latter requires two different kinds of signals, namely alarm-ON and alarm-OFF signals. Consequently, for example, in case that a vehicle in which the former vehicle alarm system is installed is remodeled to be equipped with the latter, this requires not only the change of specification of the transmitter but also of the receiver provided to the vehicle, and more specifically for example, the change of hardware configuration of the receiver, the change of software, and the like. As a result, there causes the problem that preparation and development costs for specification change are considerably increased.